China says it has newly tested more than 600 batches of liquid milk and found no traces of melamine, the chemical recently found in powdered milk that killed four babies and sickened thousands.

Chinese authorities said Sunday that milk samples from 27 cities across China all tested negative for the chemical. This was China's sixth round of testing since the tainted-milk scandal erupted last month.

Melamine-tainted products have sickened more than 54,000 Chinese children since last month. Four children have died.

The scandal has led to the arrests of 27 people in China, and the recall or prohibition of Chinese-made milk products by more than 50 nations.

Chinese-based Sanlu Group acknowledged in mid-September that its baby formula products were laced with melamine. Sanlu is a leading maker of dairy products and is partly owned by a New Zealand company, Fonterra.